Stacking apparatus and method for assembly of polymer batteries

ABSTRACT

A stacking apparatus and a method for assembly of electrochemical cells. The stacking apparatus includes at least one stacking head having an adjustable holding member adapted to hold an electrochemical laminate of a pre-determined length and means for adjusting the shape of the electrochemical laminate of the pre-determined length during stacking of a plurality of electrochemical laminates. The electrochemical laminates are assembled in a way that prevents air entrapment between the electrochemical laminates.

CROSS REFERENCE TO RELATED APPLICATION

The present application claims priority under 35 U.S.C. 120 frominternational PCT Application No. PCT/CA2003/001480 filed on Sep. 18,2003 by Parker et al. and designating the United States of America.

FIELD OF THE INVENTION

The present invention relates generally to the manufacturing of polymerbatteries and more specifically to an apparatus and method for stackingpolymer electrochemical laminates to form polymer electrochemical cellsthat are constituents of a polymer battery.

BACKGROUND OF THE INVENTION

Rechargeable batteries manufactured from laminates of solid polymerelectrolytes and sheet-like anodes and cathodes display many advantagesover conventional liquid electrolyte batteries. These advantages includelower overall battery weight, high power density, high specific energy,longer service life, as well as being environmentally friendly since thedanger of spilling toxic liquid into the environment is eliminated.

Solid polymer electrochemical cell components include positiveelectrodes, negative electrodes and a separator material capable ofpermitting ionic conductivity such as a solid polymer electrolytesandwiched between each anode and cathode. The anodes (or negativeelectrodes) and cathodes (or positive electrodes) are made of materialcapable of reversibly intercalating alkali metal ions.

Such an advanced battery system typically consists of a series ofextremely thin film laminates of anode material, polymer electrolyteseparator, cathode material and current collector assembled together asa multi-layer construction in either a flat roll configuration, a jellyroll configuration or a flat stack configuration to form a battery.Individual electrochemical laminates are typically mono-face or bi-face.A mono-face electrochemical laminate consists of a current collector, acathode, a polymer electrolyte separator, and an anode covered with aninsulating polypropylene film to insulate the electrochemical laminatefrom the adjacent one for preventing short circuits. A bi-faceelectrochemical laminate consists of a central current collector havinga cathode layer on both sides, a polymer electrolyte separator adjacenteach cathode layer, and an anode layer adjacent each electrolyteseparator. In a bi-face laminate, the insulating polypropylene film iseliminated since the risk of short-circuits between the anode and thecathode of adjacent laminates is removed. A bi-face laminate assemblytypically provides a higher energy density.

For large batteries (500 gr or more), the preferred configuration is aflat stacked multi-layer assembly of bi-face laminate for its highenergy density and for its ability to be shaped into a limited volume.

Numerous methods of assembling laminates into cells and batteries havebeen devised and/or investigated. U.S. Pat. No. 5,100,746 discloses amethod of assembling the anode, cathode, current collector andelectrolyte separator layers are co-laminated using a series of pressurerollers, the assembly thereafter being coiled to form a battery;however, the assembly could be cut and stacked.

U.S. Pat. No. 6,030,421 discloses a previously laminated mother-batterycontaining an anode of metallic lithium or sodium, a composite cathode,a polymer electrolyte that acts as a separator between the electrodes,and a current collector. The laminated mother-battery is thereaftersubjected to a sharp mechanical cutting out to give thin polymerelectrolyte batteries.

These documents disclose how to assemble the laminates themselves but donot teach precisely how to properly superpose or flat-stack thelaminates to form batteries.

U.S. Pat. No. 6,547,229 discloses a stacking apparatus and methodemploying one or more stations, each including a stationary stackingplatform or a conveyor upon which spaced-apart pucks are coupled fortravel thereon. A product delivery apparatus drives one or more movablewebs to which segmented product sheets are removably affixed. Theproduct delivery apparatus includes one or more rotatable laminationinterfaces associated with each of the stations for transferring productsheets from the webs to the pucks on a repetitive basis to produce astack of product sheets on the respective pucks. Each of the segmentedproduct sheets may define all or a portion of an electrochemical cell,the latter including layers of film or sheet material, wherein a portionof each of the layers is provided with a bonding feature. A puck neednot be in motion during the transfer of the product sheet from thelamination roll to the puck. The puck may or may not be attached to aconveyor, but the conveyor need not be in motion during the laminationor stack building process. In this case, a roller is moved across thepuck and simultaneously rotated so a point on the surface of the rollerinterfaces with the puck at the same location on each pass.

WO 02/43179 discloses an apparatus and method for rotatably cuttingand/or laminating layered structures or sheet material supported bywebs. A rotary converting apparatus and method converts a web comprisinga cathode layered structure and a web comprising an anode layeredstructure into a series of layered electrochemical cell structuressupported by a release liner. Employment of a rotary converting processprovides for the creation of a product having a finished size, withoutneed for downstream or subsequent cutting.

These two documents disclose methods of stacking components of laminatesusing a rotary device. This type of rotating mechanism is however oftenunreliable to produce precise assembly.

There are numerous difficulties to overcome when stacking extremely thinsheets together to produce electrochemical cells. First, each layer mustbe precisely aligned with the other layers in order to have a properlyassembled stack that can be electrically connected with ease and withinwhich no electrical short circuit will occur due to misalignment of theplurality of layers. A rotary system is inherently unable to provide theprecise stacking of each layer required for electrochemical cellassembly. Secondly, when stacking the various layers of theelectrochemical cell together, it is imperative that air not be trappedbetween two layers. Air entrapment will prevent proper contact betweenthe various layers thereby reducing the capacity of the electrochemicalcell as well as creating uneven surfaces that may cause further problemsin subsequent assembly steps. Thirdly, the components, i.e. thin filmsof cathode, anode and electrolyte separator, are sticky and aredifficult to handle without ripping or corrupting.

Thus there is a need in the polymer battery industry for an efficientmethod and apparatus for stacking polymer electrochemical laminates andconstituents thereof to form polymer electrochemical cells andbatteries.

STATEMENT OF THE INVENTION

It is therefore an object of the present invention to provide a stackingapparatus for assembly of electrochemical cells comprising:

-   -   a supporting structure;    -   at least one stacking head having an adjustable holding member        adapted to hold an electrochemical laminate of a pre-determined        length and having means for adjusting the shape of the        electrochemical laminate;    -   the stacking head being operative to stack a plurality of        electrochemical laminates of the pre-determined length one on        top of the other, during stacking the adjustable holding member        holding each particular electrochemical laminate of the        pre-determined length in a shape such that a central portion of        the particular electrochemical laminate of the pre-determined        length is deposited first, followed by a motion of the        adjustable holding member that progressively lowers the        remainder of the particular electrochemical laminate of the        pre-determined length, thereby preventing air entrapment between        adjacent electrochemical laminates of the pre-determined length        in the stack.

Advantageously, the adjustable holding member comprises a substantiallyflat plate made of a micro-porous material through which a vacuum systemgenerates a negative pressure that holds the pre-determined length ofelectrochemical laminate.

As embodied and broadly described, the invention further provides aprocess for assembling a plurality of electrochemical laminates to forma battery comprising the steps of:

-   -   laminating a continuous length of anode film with a continuous        length of pre-assembled half cell comprising a current        collector, a cathode film and an electrolyte separator film;    -   cutting the laminate into pre-determined lengths of laminates;    -   stacking the pre-determined lengths of laminates one on top of        the other in a shape such that a central portion of each        pre-determined length of laminate is deposited first, followed        by a motion that lowers the remainder of the pre-determined        length of laminate, thereby preventing air entrapment between        adjacent pre-determined lengths of laminate in the stack.

As embodied and broadly described, the invention also provides a processfor assembling a plurality of electrochemical laminates to form abattery wherein the electrochemical laminates are in a charged statewhen being assembled one above the other.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood and other advantages will appearby means of the following description and the following drawings inwhich:

FIG. 1 is a partial perspective view of a plurality of stackedelectrochemical laminates forming an electrochemical cell according toone embodiment of the invention;

FIG. 2 is a schematic cross-sectional view of a bi-face electrochemicallaminate according to one embodiment of the invention;

FIG. 3 is a schematic cross-sectional view of a pre-assembly of anelectrochemical laminate according to one embodiment of the invention;

FIG. 4 is a schematic front elevational view of a stacking apparatusaccording to one embodiment of the invention;

FIGS. 5A and 5B are enlarged schematic front elevational views of twoembodiments of a component of the stacking apparatus according to theinvention; and

FIGS. 6 a, 6 b and 6 c illustrate schematic front elevational views ofthree different positions assumed by the component illustrated in FIG.5A throughout one assembly cycle of the assembly process according tothe invention;

DETAILED DESCRIPTION

In FIG. 1, there is shown for illustrative purposes a specificembodiment of a Lithium polymer electrochemical cell 10 comprising aprismatic assembly of a plurality of electrochemical laminates 12stacked together. With reference to FIG. 2, in a preferredconfiguration, each individual electrochemical laminate 12 comprises acentral cathode current collector 14, a cathode film 16 and 18 layeredon both sides of cathode current collector 14, a polymer electrolyteseparator film 20 and 22 layered over each cathode film 16 and 18, andan anode thin sheet 24 and 26 layered over each polymer electrolyteseparator film 20 and 22, which together form a bi-face electrochemicallaminate 12. As shown in FIG. 2, the anode sheets 24 and 26 are offsetrelative to the central current collector 14 such that the cathodecurrent collector 14 extends on one side of the electrochemical laminate12 and the anode thin sheets 24 and 26 extend on the opposite side ofthe electrochemical laminate 12. When a plurality of laminates 12 arestacked together, the anode sheets of all laminates 12 may beelectrically connected together on one side 13 of the electrochemicalcell 10 and the cathode current collectors 14 of all laminates 12 may beelectrically connected together on the opposite side 11 of theelectrochemical cell 10 as shown in FIG. 1. Each electrochemicallaminate 12 generally has a thickness in the range of 80 to 300 microns.

In order to efficiently assemble electrochemical cell 10, the centralportion of the electrochemical laminate 12 is first assembled. Cathodefilms 16 and 18 are applied on both sides of a continuous length ofcurrent collector sheet or foil 14 which is typically a metal foil, suchas an aluminum foil, to form a continuous length of cathode films coatedon both sides of current collector 14. Subsequently, polymer electrolyteseparator films 20 and 22 are layered over each continuous length ofcathode films 16 and 18 to form the core or half-cell 25 of laminate 12.Hereafter, an anode thin sheet 26 is applied to only one side ofhalf-cell 25 of laminate 12 as illustrated in FIG. 3 to form apre-assembly 30 of laminate 12. The pre-assembly 30 therefore consistsof a continuous length comprising a central cathode current collector 14having a layer of cathode material 16 and 18 on each side thereof, eachcathode layer 16 and 18 being covered by polymer electrolyte separatorfilms 20 and 22, and one anode sheet 26 on one side of pre-assembly 30.By continuous lengths, we understand long lengths of materials extendingfrom a few meters in length to hundreds of meters in length.

The continuous length of pre-assembly 30 is then brought to a stackingapparatus where it is cut in appropriate lengths ranging from 10 cm to80 cm depending on the electrochemical cell configuration and thereafterstacked one on top of each other to form an electrochemical cell 10.

FIG. 4 illustrates schematically a stacking apparatus 40 adapted tohandle a continuous length of pre-assembly 30, cut the pre-assembly 30to length and stack the cut lengths of the pre-assembly 30 to form anelectrochemical cell 10. In a preferred embodiment, a continuous lengthof half-cell 25 is brought together with a lithium metal anode sheet 26on an assembly roll 60 which presses the lithium metal anode sheet 26onto the half-cell 25 to form the pre-assembly laminate 30. Once thelithium metal anode sheet 26 is assembled to one side of the half-cell25, one side of the pre-assembly electrochemical laminate 30 is live andby definition charged and voltage measurements may be taken to ensurethat no short-circuits occurred in the assembly. As illustrated, whenthe continuous half-cell 25 is unrolled, a protective polypropylenesheet 62 is removed. The pre-assembly laminate 30 is wound through aseries of cylindrical rolls 64 adapted to maintain the pre-assemblylaminate 30 under a pre-determined tension and brought to the stackingapparatus 40.

In a one specific embodiment, the stacking apparatus 40 comprises astacking head 45 slideably mounted on a upper girder 46 itself mountedon a fixed supporting structure 47 and adapted to move forward andbackward on the fixed supporting structure 47. The stacking head 45 isadapted to move sideways and vertically relative to the girder 46. Incombination with the forward and backward movement of the girder 46, thestacking head 45 is adapted to move along all three axes X, Y and Z. Themovements of the stacking head 45 along the various axes are effected bysliding or rolling connections and are powered by any means know to theperson skilled in the art, for example by pneumatic, hydraulic orprecision electric motors. All through the assembly process, themovements of stacking head 45 are controlled precisely by a positioningsystem of coordinates X, Y and Z. The stacking head 45 comprises a pairof holding members 48 adapted to securely hold pre-assembly laminate 30without damaging its fragile layers. Each holding member 48 is mountedonto a rotating bracket 50 rotatably mounted on the stacking head 45through a slot system 82, 84. The rotating brackets 50 are adapted tocontrol the angular positions of each holding member 48 relative to oneanother and relative to the horizontal axis. A mechanical, hydraulic orpneumatic system (not shown) controls the rotation of rotating brackets50 and therefore the angular positions of each holding member 48.

As illustrated in FIGS. 5A and 5B, holding members 48 consists of a flator curvilinear plate 52 made of a micro-porous material compatible withlithium which means that it does not adhere to the lithium sheet 26. Theupper portion of plate 52 comprises a vacuum chamber 56 that isconnected through the rotating brackets 50 to a pneumatic vacuum system,via a conduit 58. In operation, the vacuum system generates a vacuumwithin vacuum chamber 56, which in turn generates a negative pressure onthe lower surface 70 of plate 52 through the micro-pores or capillariesof the micro-porous material such that the holding member 48 can liftand securely hold the pre-assembly laminate 30. The micro-pores of thematerial ensures that the pre-assembly laminate 30 and more specificallythe upper lithium sheet 26 will not be damaged by the vacuum forceapplied thereto. If plate 52 comprised a series of small aperturesthrough which the vacuum force was applied, the lithium sheet 26 couldbe deformed to a mirror image of plate 52 which would be detrimental tothe subsequent assembly of the electrochemical cell 10. The micro-poresare sufficiently small that the vacuum force does not affect the surfaceof the lithium sheet 26.

Referring back to FIG. 4, in operation, an end 42 of the continuouslength of pre-assembly laminate 30 is gripped by a pincer 44 having softjaws with flat surfaces which then pulls a pre-determined length of thepre-assembly laminate 30 into position in front of stacking head 45 andonto a smooth surface 72 located immediately in front of stacking head45. Aligned with the end of surface 72, a rotary knife 76 and anvil 74assembly is provided. Rotary knife 76 and anvil 74 are adapted to movetogether perpendicular to the end of surface 72 to effectively cut thepre-assembly laminate 30 to its pre-determined length. In operation, thestacking head 45 is moved forward over pre-assembly laminate 30 andsurface 72 and is lowered onto the pre-assembly laminate 30 which itholds securely onto surface 72 while the rotary knife 76/anvil 74assembly is rolled onto the pre-assembly laminate 30 to cut thepre-assembly laminate 30 to a pre-determined length. Thereafter, thestacking head 45 lifts the cut pre-assembly 30 using the negative forcegenerated on the lower surface 70 of holding members 48 by the vacuumsystem through vacuum chamber 56.

Stacking head 45 is then moved forward and is positioned over a carriageplatform 80. The surface 86 of the carriage platform 80 is treated withplasma deposition to prevent the pre-assembly laminate 30 from stickingto it. Stacking head 45 then moves down and deposits the pre-assemblylaminate 30 onto the carriage platform 80 to form the first layer of theelectrochemical cell 10. Stacking head 45 then moves back to its initialposition where the cycle previously described is repeated. A secondpre-assembly laminate 30 is deposited onto the previously laidpre-assembly laminate 30 to form a complete bi-face electrochemicallaminate 12 as illustrated in FIG. 2. The cycle is repeated until apredetermined number of electrochemical laminates are assembled to forman electrochemical cell 10. The carriage platform 80 is then moved toanother station (not shown) for further processing; an empty carriageplatform 80 is positioned in its place and the entire cycle is repeatedfor assembling a new electrochemical cell 10.

FIG. 6 illustrates the various positions holding members 48 assume atvarious points during the assembly cycle. FIG. 6 a illustrates theposition of the holding members 48 when stacking head 45 is lowered ontothe pre-assembly laminate 30 to hold it securely onto surface 72 whileit is being cut to the pre-determined length. The holding members 48form between them a substantially flat surface with an angle ofapproximately 180°. At this stage, the vacuum system is turned on whichgenerates a negative pressure at the surface 70 which enables holdingmembers 48 to gently lift the cut length of laminate 30. Thereafter, theholding members 48 assume the position illustrated in FIG. 6 b, wherethe rotating brackets 50 are rotated inwardly such that the holdingmembers 48 form between them an angle of less the 180° and thepre-assembly laminate 30 assumes a somewhat angular or curvilinearshape. The rotating brackets 50 are pivoted or rotated via preciselyshaped slots 82 and 84 to prevent the surfaces 70 of the holding members48 from moving marginally away from each other and creating a pullingforce on the pre-assembly laminate 30 that could rip or damage it. Thepre-assembly laminate 30 is carried to a position above the carriageplatform 80 onto which another pre-assembly laminate 30 has beenpreviously laid down. The stacking head 45 lowers the pre-assemblylaminate 30 onto the previously laid component in this angular orcurvilinear position such that the central or middle portion of laminate30 touches the previously laid component first. The rotating brackets 50are then rotated outwardly as shown in FIG. 6 c, in order to lower andat the same time spread the remainder of the pre-assembly laminate 30onto the previously laid component thereby driving out air andpreventing air entrapment between the components during assembly.Simultaneously, the negative pressure is released from vacuum chambers56 to release the pre-assembly 30 while it is being spread onto thepreviously laid component. Stacking head 45 then moves back to itsinitial position where the entire cycle previously described is repeateduntil the predetermined number of electrochemical laminates areassembled to form an electrochemical cell 10. When the predeterminednumber of assembled electrochemical laminates is reached, the carriageplatform 80 is moved away and replaced with an empty one and theassembly cycle begins again.

Stacking apparatus 40 is shown and described with a single stacking head45; however, a plurality of stacking heads 45 may be installed side byside in the supporting structure 47 such that a plurality ofelectrochemical cells 10 may be assembled simultaneously. In thisembodiment, there are as many rotary knife 76/anvil 74 assemblies asthere are stacking heads 45. The continuous length of pre-assemblylaminate 30 is gripped by the pincer 44 and pulls a pre-determinedlength of the pre-assembly laminate 30 into position in front of theplurality of stacking heads 45 and onto a plurality of aligned smoothsurfaces 72 located immediately in front of each of the plurality ofstacking heads 45. One rotary knife 76/anvil 74 assembly is positionedadjacent each of the plurality of stacking heads 45. In operation, thestacking heads 45 are then moved forward over the length of pre-assemblylaminate 30 and are lowered onto the pre-assembly laminate 30 which itholds securely onto surfaces 72 while the rotary knife 76/anvils 74assemblies are rolled onto the pre-assembly laminate 30 adjacent eachstacking head 45 to cut the pre-assembly laminate 30 to pre-determinedlengths. Thereafter, the stacking heads 45 lift their respective portionof the cut pre-assembly laminate 30 as previously described and stackthem onto a plurality of carriage platforms 80, one for each stackinghead 45 in the same manner previously described. In this embodiment ofthe stacking apparatus 40, the movements of the plurality of stackingheads 45 are also controlled precisely by a positioning system ofcoordinates X, Y and Z throughout the assembly process.

Although the present invention has been described in relation toparticular variations thereof, other variation and modifications arecontemplated and are within the scope of the present invention.Therefore the present invention is not to be limited by the abovedescription but is defined by the appended claims.

1. A stacking apparatus for assembly of electrochemical cellscomprising: a supporting structure; at least one stacking head operativeto stack a plurality of electrochemical laminates of a pre-determinedlength one on top of the other, said stacking head having at least oneadjustable holding member adapted to hold a particular one of theelectrochemical laminates and having means for adjusting the shape ofthe particular one of the electrochemical laminates, said at least oneadjustable holding member being operative during stacking to hold theparticular one of the electrochemical laminates in a shape such that acentral portion of the particular one of the electrochemical laminatesis deposited first and to subsequently move so as to progressively lowerthe remainder of the particular one of the electrochemical laminates,thereby preventing air entrapment between adjacent ones of theelectrochemical laminates being stacked.
 2. A stacking apparatus asdefined in claim 1, wherein said at least one adjustable holding memberincludes a vacuum system for generating a negative pressure for holdingthe particular one of the electrochemical laminates.
 3. A stackingapparatus as defined in claim 2, wherein said at least one adjustableholding member includes a plate made of a micro-porous material, saidvacuum system being operative for generating the negative pressurethrough said plate.
 4. A stacking apparatus as defined in claim 3,wherein said at least one adjustable holding member includes a vacuumchamber positioned adjacent said plate of micro-porous material.
 5. Astacking apparatus as defined in claim 1, further comprising mechanicalcutting means adjacent said stacking head and adapted to cut acontinuous length of electrochemical laminate to said pre-determinedlength.
 6. A stacking apparatus as defined in claim 5, wherein saidmechanical cutting means includes a rotary knife.
 7. A stackingapparatus as defined in claim 1, wherein said at least one stacking headincludes two adjustable holding members rotatably mounted onto said atleast one stacking head.
 8. A stacking apparatus as defined in claim 7,wherein said two adjustable holding members are rotatably mountedthrough a slot system for guiding the rotational movement of said twoadjustable holding members, thereby preventing damage to the particularone of the electrochemical laminates.
 9. A stacking apparatus as definedin claim 1, wherein said at least one stacking head is movablevertically and horizontally within said supporting structure.
 10. Astacking apparatus as defined in claim 1, comprising a plurality ofstacking heads mounted side by side on said supporting structure suchthat a plurality of electrochemical cells may be assembledsimultaneously.
 11. A stacking apparatus as defined in claim 1, furthercomprising a treated surface for stacking thereon the plurality ofelectrochemical laminates of the pre-determined length.
 12. A stackingapparatus as defined in claim 1, further comprising at least onecarriage platform having a treated surface for stacking thereon theplurality of electrochemical laminates of the pre-determined length.